Skin girth is a measurement

Measurement

Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...

 of a yacht

Yacht

A yacht is a recreational boat or ship. The term originated from the Dutch Jacht meaning "hunt". It was originally defined as a light fast sailing vessel used by the Dutch navy to pursue pirates and other transgressors around and into the shallow waters of the Low Countries...

 hull

Hull (watercraft)

A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

.

Skin girth is specified in some design rules to handicap or match the capabilities of sailing vessels

Sailboat

A sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...

 of similar design such as the 12 metre boats. Skin girth is measured by following the surface of the hull from a given elevation on the hull vertically from a specified fore-and-aft position. It differs from the chain girth

Chain girth

Chain girth is a measurement of a yacht hull.Chain girth is specified in some design rules to handicap or match the capabilities of sailing vessels of similar design such as the 12 metre boats...

which follows the skin on convex surfaces, but goes straight across the chord of concave surfaces, as a tight chain would.